In-building radio frequency communications system with automatic failover recovery

ABSTRACT

An improved in-building radio frequency communications system with automatic failover recovery comprising a primary external antenna and one ancillary external antenna, each antenna directed to a primary transmission tower and to an ancillary transmission tower, respectively, and a diversity site donor system capable of monitoring the strength and/or quality of the radio frequency signals received from the primary transmission tower and switching communications between the primary transmission tower and the ancillary transmission tower based on the strength and/or quality of the radio frequency signals received from the primary transmission tower.

CROSS REFERENCE TO RELATED APPLICATION

This application is a divisional of U.S. Ser. No. 11/030,646, filed Jan.4, 2005 and currently pending in Art Group 2617, entitled In-BuildingRadio Frequency Communications System With Automatic Failover Recovery,which is hereby incorporated by reference.

FIELD OF THE INVENTION

The invention relates to the field of in-building radio communicationcoverage enhancement. Specifically, the invention provides a solution tomaintain radio communication coverage inside a facility when the primaryradio transmission tower providing the radio communication signals tothe in-building system fails or is taken out of operation formaintenance or service. The invention will detect that the signals fromthe primary transmission tower are not viable and automatically connectradio communication signals from an alternate transmission tower to thein-building system electronics and signal distribution system.

BACKGROUND OF THE INVENTION

Wireless communication devices, such as cell phones and two-way radios,are becoming ever more popular. Such devices typically receive andtransmit radio frequency (RF) signals from and to remote RF signaltransmission towers, such as cell towers. While RF signals are capableof penetrating solid objects, the strength and quality of those signalsdegrade as more barriers are present between the transmission tower andthe wireless communication device. Signal degradation is especiallyacute within structures, such as office buildings or factories, whichoffer multiple barriers between the transmission tower and the wirelesscommunication device.

In-building radio frequency communications systems have been developedto improve performance of wireless communication devices withinstructures. These systems typically use a strategically located anddirected antenna, which typically is located on the exterior of thestructure (roof or side wall), providing a communications link with a RFsignal transmission tower. The directed antenna is focused at a specificRF signal transmission tower (primary RF signal donor site) in an effortto maximize desired signal levels from the donor site to the in-buildingsystem. In addition, the directed antenna will minimize the level ofnon-desired and interference producing signals that arrive at angles,relative to the direction that the external antenna is focused, outsidethe horizontal beamwidth of the external antenna. The desired effect ofthe directed antenna is to isolate the in-building system from all RFsignals other than those used at the primary donor site. They also useone or more low profile antennas located within the interior of thestructure, strategically placed to provide coverage in areas where theRF signal levels and/or quality are not adequate to support reliabletransmissions. The internal antennas are linked together by aninfrastructure comprised of coaxial, fiber optic and/or network cablesand power splitters. The infrastructure is typically connected with theexternal antenna through a bi-directional amplifier (BDA), a device thatincreases the strength of the signal passing through it, either as thesignal is received from the transmission tower to be transmitted to thewireless communication device (the signal downlink) or as the signal isreceived from the wireless communication device to be transmitted to thetransmission tower (the signal uplink). In such a system, the RF signalsare 1) received from the transmission tower by the external antenna andconnected to the BDA; 2) amplified by the BDA; 3) distributed via thesystem infrastructure to the internal antennas, whose quantity andlocation inside the facility are appropriate to meet systemrequirements; and 4) radiated at a sufficient level to support reliableradio communications. The net effect is to allow the signals to passbetween the transmission tower and the external antenna and between thewireless communication device and the internal antennas with relativelyfew intervening barriers. This minimization of intervening barriers,together with the signal amplification provided by the BDA greatlyimproves in-building performance of wireless communication devices.

In-building radio frequency communications systems are well known in theprior art, and may be implemented in any number of ways. See, e.g.,Point-To-Multipoint Digital Radio Frequency Transport, U.S. Pat. No.6,704,545 (Wala), issued Mar. 9, 2004; Communication System ComprisingAn Active-Antenna Repeater, U.S. Pat. No. 5,832,365 (Chen, et al.),issued Nov. 3, 1998; Method Of Locating A Mobile Station In A MobileTelephone, U.S. Pat. No. 5,634,193 (Ghisler), issued May 27, 1997.However, while these systems are designed to handle the communicationswithin a building, they all depend on reliable signals from the radiofrequency transmission tower to support in-building transmissions. Thus,in-building signal enhancement tends to be susceptible to failure ifthere is an interruption or degradation of service at the external radiofrequency transmission tower. This may result from a mechanical failure,a planned maintenance shutdown, environmental factors such as alightning strike, or other causes, most of which are beyond the controlor even awareness of the end use of the wireless communications device.In-building radio frequency communications systems known in the priorart are unable to recover from such interruptions and thus fail toprovide the level of quality and reliability desired by end users.

One class of in-building frequency communications system known in theart does exemplify some failure recovery properties. Where anomni-directional antenna is used as the external antenna for anin-building system, by design the omni-directional antenna sends andreceives RF signals equally in the horizontal plane, compared to adirectional antenna, which will focus RF energy from approximately 15°to 100° of the horizontal plane. When an omni-directional antenna isused as the external antenna for an in-building system, there may besome degree of radio frequency transmission site diversity due to theinherent ability of the omni-directional antenna to transmit/receive RFsignals equally in the horizontal plane. Under this scenario, signalsfrom more than one radio frequency transmission tower may be connectedinto the in-building system and if signals from one radio frequencytransmission tower fail, signals from a different radio frequency towermay be available to provide a level of coverage inside the facility.However, this configuration does not allow for specific redirection forprecise control over alternative RF signal sources. The presentinvention, by placing such control with the system designer, is animprovement over in-building systems that have been designed to provideradio frequency transmission tower diversity through the use of anomni-directional external antenna.

The present invention is directed to an in-building radio frequencycommunications system with the capability to automatically transfer RFsignals to the in-building system from multiple radio frequencytransmission towers. As such, it offers improved RF signal accessreliability over known systems.

It is an object of this invention to provide a fault tolerantin-building radio frequency communications system which minimizesdisruptions due to failure of the RF signals from the primary radiofrequency transmission tower.

It is a further object of this invention to provide a donor sitediversity system which continuously detects the strength and quality ofRF signals from a primary radio frequency transmission tower in order toautomatically switch an in-building radio frequency communicationssystem to an ancillary radio frequency transmission tower whenever thestrength and quality of RF signals from a primary radio frequencytransmission tower fall below an acceptable threshold.

Other objects of this invention will be apparent to those skilled in theart from the description and claims which follow.

SUMMARY

The present invention is directed to an in-building radio frequencycommunications system with fault tolerant capability when RF signalsfrom the primary radio frequency transmission tower are compromised orfail. Specifically, the invention relates to an improved system whichincorporates into an in-building radio frequency communications system aprimary external antenna and an ancillary external antenna, with theprimary external antenna oriented to receive and transmit RF signalsfrom and to a primary transmission tower, and the ancillary externalantenna oriented to receive and transmit RF signals from and to theancillary transmission tower.

The present invention further integrates an RF signal detection andswitching mechanism into the in-building radio frequency communicationssystem, the said detection and switching mechanism having twofunctions: 1) the detection mechanism constantly monitors the strengthand quality of the RF signals received from the primary transmissiontower; and 2) whenever the strength and/or quality of those RF signalsdeteriorates below a certain threshold, the switching mechanismredirects communications for the in-building radio frequencycommunications system to the ancillary transmission tower. Theredirection of communication signals is achieved by toggling a switchwithin the switching mechanism, resulting in the circuit between thein-building system and the primary external antenna being interruptedand the circuit between the in-building system and the ancillaryexternal antenna being completed, thereby establishing communicationswith the ancillary transmission tower. When the switching mechanismdetects sufficient signal quality and/or strength in the RF signalsreceived from the primary transmission tower, the switch is toggled tocomplete the circuit between the in-building system and the primaryexternal antenna and to interrupt the circuit between the in-buildingsystem and the ancillary external antenna, thereby re-establishingcommunications with the primary transmission tower.

The above-described improvements to in-building radio frequencycommunications systems increase the reliability of communications in theevent of disruptions from the primary transmission tower. Byautomatically redirecting the RF signal to a different transmissiontower having sufficient performance criteria, the invention minimizescommunications interruptions to in-building users of the system,achieving high levels of overall fault tolerance in the system.

Other features and advantages of the invention are described below.

DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic drawing depicting the basic components of thepresent invention, including a donor site diversity system.

FIG. 2 is a schematic drawing depicting the basic components of thepresent invention, together with detail of the components comprising thedonor site diversity system.

FIG. 3 is a flowchart showing the process for determining which RFsignal transmission tower should be used when the in-building radiofrequency communication system comprises a primary external antenna anda single ancillary external antenna.

DESCRIPTION OF THE INVENTION

The invention is an improvement on known in-building radio frequencycommunications systems designed to be installed and used withinstructures, such as office buildings, power generation plants,correctional facilities, etc. The basic in-building system is comprisedof the following components: a primary external antenna 32, an ancillaryexternal antenna 34, an internal antenna 30, a donor site diversitysystem 10, and a bi-directional amplifier 20. These components arenetworked together to form the in-building radio frequencycommunications system. In one embodiment, the donor site diversitysystem 10 is connected with the primary external antenna 32 and with theancillary external antenna 34 by coaxial cables and/or fiber opticcables, and the bi-directional amplifier 20 is connected with the donorsite diversity system 10 and with the internal antenna 30 by coaxialcables and/or fiber optic cables. This configuration is shown in FIG. 1.

The primary external antenna 32 must be configured to receive andtransmit RF signals 5, which are used for communications with cellphones, two-way radios, and the like. The primary external antenna 32typically should be located on the exterior of a structure where it canbe directed to a primary RF signal transmission tower 42, such that theprimary external antenna 32 is capable of transmitting and receiving RFsignals 5 to and from the primary RF signal transmission tower 42. Inthe preferred embodiment, the primary external antenna 32 is located onthe roof of the structure, or other location with an unobstructed pathto the primary RF signal transmission tower 42. The primary RF signaltransmission tower 42 is selected as providing the strongest and/orhighest quality RF signal 5 available to connect with the in-buildingradio frequency communications system.

The ancillary external antenna 34 must also be configured to receive andtransmit RF signals 5. The ancillary external antenna 34 typicallyshould be located on the exterior of the structure where it can bedirected to an ancillary RF signal transmission tower 44, such that theancillary external antenna 34 is capable of transmitting and receivingRF signals 5 to and from the ancillary RF signal transmission tower 44.Because the ancillary external antenna 34 is directed to an ancillary RFsignal transmission tower 44 generating RF signals 5 which when receivedare of a lower strength and/or quality than the RF signals 5 generatedby the primary RF signal transmission tower 42, the ancillary externalantenna 34 may be required to be of higher gain and greater directivity;for example, the ancillary external antenna 34 may be a parabolicgrid-type antenna, whereas the primary external antenna 32 may be oflower gain and directivity, such as a corner reflector or yagi typeantenna. Other types of higher gain and greater directivity antennas mayalso be used. Use of a higher gain and greater directivity ancillaryexternal antenna 34 increases the likelihood that the RF signals 5received from the ancillary RF signal transmission tower 44 and passedon to the bi-directional amplifier 20 will be of comparable strength andquality as those received from the primary RF signal transmission tower42. In the preferred embodiment, the ancillary external antenna 34 islocated on the roof of the structure. The ancillary RF signaltransmission tower 44 is selected as providing the next strongest and/orhighest quality RF signal 5 available to the in-building radio frequencycommunications system, after the primary RF signal transmission tower42.

The internal antenna 30 must be configured to receive and transmit RFsignals 5. The internal antenna 30 is typically a low-profile antennawith a power output significantly less than that of the primary 42 andsecondary 44 radio transmission towers. The internal antenna(s) 30typically is located within the interior of the structure where it iscapable of transmitting and receiving RF signals 5 to and from wirelesscommunication devices 50 located within the structure. In the preferredembodiment, multiple internal antennas 30 are located within thestructure, with each internal antenna 30 configured to receive andtransmit RF signals 5. The multiple internal antennas 30 are distributedthroughout the interior of the structure so as to provide the greatestpractical coverage within the structure, such that each of the internalantennas 30 is capable of transmitting and receiving RF signals 5 to andfrom nearby wireless communication devices 50. Each of the internalantennas 30 is connected with the bi-directional amplifier 20, eitherdirectly or indirectly via a network of cables. In the preferredembodiment, the network connecting the internal antennas 30 is comprisedof coaxial cables, although other infrastructure configurations exist,such as fiber optic and network (CAT5/6) cable type systems.

The bi-directional amplifier 20 may be any type of RF signal amplifierknown in the art capable of increasing the strength of RF signals 5. Thebi-directional amplifier 20 must be capable of increasing the strengthof RF signals 5 downlinked from RF signal transmission towers to betransmitted to personal communications devices, and capable ofincreasing the strength of RF signals 5 uplinked from wirelesscommunication devices to be transmitted to RF signal transmissiontowers. The bi-directional amplifier 20 is connected with the donor sitediversity system 10, from which it receives the downlinked RF signals 5and to which it sends uplinked RF signals 5, and is connected with theinternal antenna 30, from which it receives the uplinked RF signals 5and to which it sends downlinked RF signals 5. In the preferredembodiment, the bi-directional amplifier 20 is located proximate to thedonor site diversity system 10.

The donor site diversity system 10 is connected with the primaryexternal antenna 32 and with the ancillary external antenna 34. Thedonor site diversity system 10 monitors the strength and quality of theRF signals 5 received by the primary external antenna 32 from theprimary RF signal transmission tower 42. The donor site diversity system10 is further capable of switching the communication connection betweenthe primary RF signal transmission tower 42 and the ancillary RF signaltransmission tower 44, based on the strength and quality of the RFsignals 5 received from the primary RF signal transmission tower 42.

In one embodiment, the donor site diversity system 10 comprises aprimary circuit 12, an ancillary circuit 14, a RF signal switch 16, anda RF signal detector/sensor 18. This configuration is shown in FIG. 2.

The primary circuit 12 is configured to establish a communicationsconnection between the primary external antenna 32 and thebi-directional amplifier 20 such that RF signals 5 may travel betweenthe primary external antenna 32 and the bi-directional amplifier 20. Theancillary circuit 14 is configured to establish a communicationsconnection between the ancillary external antenna 34 and thebi-directional amplifier 20 such that RF signals 5 may travel betweenthe ancillary external antenna 34 and the bi-directional amplifier 20.The primary circuit 12 and the ancillary circuit 14 are mutuallyexclusive; that is, when the primary circuit 12 is active, the ancillarycircuit 14 is inactive, and RF signals 5 are received by and sent fromthe in-building radio frequency communications system solely through theprimary circuit 12; and when the ancillary circuit 14 is active, theprimary circuit 12 is inactive, and RF signals 5 are received by andsent from the in-building radio frequency communications system solelythrough the ancillary circuit 14.

The RF signal switch 16 is configured to activate and deactivate theprimary circuit 12 and to activate and deactivate the ancillary circuit14. In the preferred embodiment, the RF signal switch 16 toggles aninterlink 17 between the primary circuit 12 and the ancillary circuit14, such that the ancillary circuit 14 is interrupted when the interlink17 is toggled to and completes the primary circuit 12, and the primarycircuit 12 is interrupted when the interlink 17 is toggled to andcompletes the ancillary circuit 14.

The RF signal detector/sensor 18 is configured to monitor the strengthand quality of the RF signals 5 received from the primary RF signaltransmission tower 42. In one embodiment, the RF signal detector/sensor18 comprises a monitoring means and a logic processor appropriate to thetarget RF signals 5 enhancing the in-building environment. Themonitoring means is configured to monitor the strength and quality ofthe RF signals 5 received from the primary RF signal transmission tower42. In the preferred embodiment, the monitoring means is configured tocontinuously monitor the strength and quality of the RF signals 5received from the primary RF signal transmission tower 42. The logicprocessor of the RF signal detector/sensor 18 is connected with the RFsignal switch 16, and is configured to determine the sufficiency of thestrength and quality of the RF signals 5 received from the primary RFsignal transmission tower 42. The threshold criteria for determining thesufficiency of the strength and quality of the RF signals 5 may bepreset, or altered by the user, or dynamically altered automaticallydepending on environmental criteria. The logic processor compares thesufficiency of the strength and quality of the RF signals 5 against thethreshold criteria, and communicates a positive signal to the RF signalswitch 16 if the sufficiency of the strength and quality of the RFsignals 5 meets or exceeds the threshold criteria, and communicates anegative or ground signal to the RF signal switch 16 if the sufficiencyof the strength and quality of the RF signals 5 fails to meet or exceedthe threshold criteria. The RF signal switch 16 in turn toggles theinterlink 17 to complete the primary circuit 12 when a positive signalis received, thereby interrupting the ancillary circuit 14, and togglesthe interlink 17 to complete the ancillary circuit 14 when a negativesignal is received, thereby interrupting the primary circuit 12. Thisprocess is shown in FIG. 3.

In one embodiment, the donor site diversity system 10 further comprisesa signal splitting means for directing RF signals 5 to both the RFsignal detector/sensor 18 and the RF signal switch 16. In the preferredembodiment the signal splitting means comprises an unequal power signalsplitter 60, a two-way power divider 64, and a variable attenuator 68.The unequal power signal splitter 60 further has an input port 61, ahigh power output port 62, and a low power output port 63. The two-waypower divider 64 further has an input port 65, a first equal powerdistribution output port 66, and a second equal power distributionoutput port 67. The unequal power signal splitter 60 is located in-linewith the primary circuit 12, whereby the unequal power signal splitter60 is in connection with the primary external antenna 32 through theinput port 61 of the unequal power signal splitter 60, the unequal powersignal splitter 60 is in connection with the RF signal switch 16 throughthe high power output port 62 of the unequal power signal splitter 60,and the unequal power signal splitter 60 is in connection with thetwo-way power divider 64 through the low power output port 63 of theunequal power signal splitter 60 and into the input port 65 of thetwo-way power divider 64. RF signals 5 from the primary external antenna32 enter the unequal power signal splitter 60 through its input port 61and are directed simultaneously to the RF signal switch 16 and thetwo-way power divider 64. The two-way power divider 64 in turn is inconnection with a test port through the first equal power distributionoutput port 66 of the two-way power divider 64 and with the variableattenuator 68 through the second equal power distribution output port 67of the two-way power divider 64. The variable attenuator 68 is inconnection with the RF signal detector/sensor 18. The variableattenuator 68 is used to adjust the threshold level of the RF signaldetector/sensor 18. RF signals received by the primary external antenna32 are transmitted along the primary circuit 12 to the unequal powersignal splitter 60, whereby the RF signals 5 are then split between theRF signal switch 16 and the RF signal detector/sensor 18 (the latter byway of the two-way power divider 64 and variable actuator 68). In usingthe combination of the unequal power signal splitter 60 and the two-waypower divider 64 to send RF signals 5 to the RF signal switch 16 and theRF signal detector/sensor 18, the monitoring means of the donor sitediversity system 10 can monitor the strength and/or quality of the RFsignals 5 received from the primary RF signal transmission tower 42 on acontinuous basis. The RF signal detector/sensor 18 then directs the RFsignal switch 16 to toggle between the primary circuit 12 and theancillary circuit 14 as appropriate.

Modifications and variations can be made to the disclosed embodiments ofthe invention without departing from the subject or spirit of theinvention as defined in the following claims.

1. An in-building radio frequency communications system comprising aprimary external antenna, suitably configured to receive and transmitradio frequency signals, said primary external antenna located on anexterior of a structure and oriented towards a primary radio frequencysignal transmission tower such that the primary external antenna iscapable of transmitting and receiving radio frequency signals to andfrom the primary radio frequency signal transmission tower; an ancillaryexternal antenna, suitably configured to receive and transmit radiofrequency signals, said ancillary external antenna located on theexterior of the structure and oriented towards an ancillary radiofrequency signal transmission tower such that the ancillary externalantenna is capable of transmitting and receiving radio frequency signalsto and from the ancillary radio frequency signal transmission tower; adonor site diversity system, in connection with the primary externalantenna and with the ancillary external antenna, said donor sitediversity system suitably configured to monitor the strength and qualityof the radio frequency signals received from the primary radio frequencysignal transmission tower and capable of switching between the primaryradio frequency signal transmission tower and the ancillary radiofrequency signal transmission tower based on the strength and quality ofthe radio frequency signals received from the primary radio frequencysignal transmission tower; an internal antenna, suitably configured toreceive and transmit radio frequency signals, said internal antennalocated within an interior of the structure such that the internalantenna is capable of transmitting and receiving radio frequency signalsto and from one or more wireless communication devices located withinthe structure; and a bi-directional amplifier, in connection with thedonor site diversity system and with the internal antenna, saidbi-directional amplifier suitably configured to increase the strength ofradio frequency signals received from the radio frequency signaltransmission towers through the external antennas and received from theone or more wireless communication devices through the internal antenna;wherein the primary external antenna and the ancillary external antennaare suitably configured such that both the primary external antenna andthe ancillary external antenna are capable of operating independentlyfrom the other, where at any given time only one of said primary andancillary external antennas is receiving or transmitting radio frequencysignals for the purpose of providing a communications link between oneof the radio frequency signal transmission towers and the one or morewireless communication devices, while the other of said primary andancillary external antennas is in stand-by mode whereby it is notproviding a communications link between either of the radio frequencysignal transmission towers and the one or more wireless communicationdevices.
 2. The in-building radio frequency communications system ofclaim 1 wherein the donor site diversity system is connected with theprimary external antenna and with the ancillary external antenna bycoaxial cables and/or fiber optic cable, and the bi-directionalamplifier is connected with the donor site diversity system and with theinternal antenna by coaxial cables and/or fiber optic cable.
 3. Thein-building radio frequency communications system of claim 1 furthercomprising multiple internal antennas, each internal antenna suitablyconfigured to receive and transmit radio frequency signals, with themultiple internal antennas distributed throughout the interior of thestructure, such that each of the internal antennas is capable oftransmitting and receiving radio frequency signals to and from wirelesscommunication devices located within the structure, and with each of theinternal antennas in connection with the bi-directional amplifier;wherein the multiple internal antennas are suitably configured such thateach of the multiple internal antennas is capable of operatingindependently from each other of the multiple internal antennas for thepurpose of providing a communications link between one of the radiofrequency signal transmission towers and the one or more wirelesscommunication devices.